Compensating condenser



\ NOV. 7, 1939., E, E MAXHAM 2,179,417

COMPENSATING CONDENSER Filed Oct. 50, 1957 fzz/ ME. 77m j ifwfzg Ma MJ parts and are quite expensive. 50 vention provides a simple inexpensive solution Patented Nov., 79 i939 UNITED STATES MNM? PATENT OFFICE 2,179,4lll

QMPENSATING CONDENSER Application October 30, 1937, Serial No. 172,005

3 Claims.

This invention relates to a novel thermally responsive compensating condenser for Vradio receivers and the like. The principal object Of the invention is'to provide a simple compensating 5 condenser structure which is adapted to vary its capacity in response to temperature variations that occur during the operation of a radio receiver, .which capacity variation may be used to compensate for other variations in the inductance or capacitance or both of other elements in the receiver and thus prevent variation in the tuning of the receiver due to such temperature variations. A

A furtherobject of the invention is to provide l5 a novel condenser of this type which is not susceptible to microphonic action and, therefore, cannot act as a source of undesirablemicrophonic noises.

In the modern superheterodyne radio receiver,

2o it is essential that the tuning of the local oscillator be precisely maintained in order to prevent drift of the receiver away from the carrier wave signal to which it is tuned. This is particularly important in the types of modern receivers which are equipped with so-called automatic tuning, that is Vmeans for eiecting tuning of the receiver by the use of push-button controls or other such devices. In such receivers, the tuning is eiected automatically in response to a simple operation by the user, such as the depressing of a selected push-button corresponding tothe desired broadcast signal. It is characteristic of the tuned circuit elements now employed, `such as padding condensers, tube sockets, etc., that their capacity tends to change with temperature variations and, since a receiver is frequently tuned automatically at times when the temperature of the receiver elements is varying, for example when the receiver is rst turned on, there is a tendency for.the receiver toY drift due to the variation in capacity of the tuned circuit elements. To a lesser extent, variations in inductancewill also obtain. This has been overcome by the employment of automatic frequency control devices whose purpose is to prevent variation in the tuning of the receiver or, in other words, to prevent drifting of the receiver. However, such circuits require a considerable number of extra The present int0 the problem ofwdrift.

The present invention provides a simple comc pensating condenser which is adapted particularly for use in the oscillator circuit and which eiec- 55 tively prevents the undesirabledetuning of the the condenser.

(Cl. )W5-41.5)

oscillator due to variations in temperature. Moreover, this device is so constructed that it is substantially incapable of vibrating in response to extraneous mechanical vibrations and, therefore, it cannot act as a source of microphonic 5 noises which has been a serious defect of prior condenser structures.

The invention may be more fully understood by reference to the` accompanying drawing, in which- 10 Fig. l is a face View of the device; and

Fig. 2 is a sectional view taken along line 2-2 of Fig. 1.

Referring to the drawing, there isprovided a rigid cup-shaped metallic member I which is 15 adapted to form a fixed element of the condenser. This member has a recessed portion 2 surrounded by an annular face 2a, and a centrally located annular projection or ilange 3. At its outer portion, the member has a flange 4 which has an 20 integrally formed extension 5 adapted to serve as a supporting element andas a ground terminal. By means of the supporting element 5, the condenser structure may be attached to the grounded chassis of a radio receiver, thus grounding the 25 member i.

The central recessed portion 2 is seated upon an insulating support 6 with the ange 3 extending into a central recess 'I of the support. The support 6 may be formed ofany suitable mate- 30 rial such as Isolantite or other ceramic material. An insulating sleeve or bushing 8, which may be formed of the same material, has one end extending Within the angev 3 and serves to insulate the member l from the screw 9 which eX- 35 tends through the sleeve 8 and through the support 6. The screw 9 serves to secure a thermally responsive metallic disk I0 which is supported on the extending end of the sleeve 8. The coating portions of the elements 3, 6 and 8 are so con- 40 structed and arranged that they are held together as a unit by means of a forced t between the ange 3 and the support 6 a'nd between the sleeve 8 and theelange 3. The disk I0 is, of course, readily removable by loosening and re- 45 moving the screw 9. At the opposite end of the screw 9 there is provided a terminal Il by means of which electrical connection is made to the disk l0.

The disk i0, which is preferably formed of bimetallic material, serves as the other element of This disk is so constructed that when it is secured at its central portion by means of the screw 9 with its peripheral edge free, and when it is subjected to increasing temperature,

its peripheral portion tends to flex away from the member l, as illustrated by the broken line representation in Fig. 2. A suitable bimetallic disk is one composed of a layer of brass and a layer of Invar bonded together and positioned with the brass face on the inside of the cup l. Actually, the thermally-responsive disk il) will tend to bend about a diametrical line so that opposite portions of the periphery of the disk will flex as illustrated. Thus, the condenser varies its capacity in response to ambient temperature variations and compensates for changes in capacity and/or inductance in the tuned circuit which would otherwise cause detuning of the circuit. By properly designing the device, it may be caused to substantially eliminate detuning of the circuit with which it is associated.

Since the compensating condenser may be employed in the oscillator circuit it is extremely important that its capacity be independent of mechanical vibration, or in other words, the condenser must be non-microphonic. In accordance with the invention, this feature obtains by the use of a circular thermo-responsive plate or disk rigidly mounted at its center. Experimental results have shown that one plate of a conventional padding condenser cannot be replaced by a bimetallic plate to form a compensating condenser, capable of meeting the non-microphonic requirements. The circular disk supported at the center has the advantage that it is substantially incapable of vibrating in response to mechanical vibrations of the receiver chassis, and thus is non-microphonic. Hence, although the plate or disk will iiex in response to variations in ambient temperature, it will not vibrate when mechanically excited.

An important feature of the invention is the dishing of the central recessed portion 2 to provide a wide clearance between the center part of the electrode i0 and the grounded cup. In this way, the residual capacity of the device is minimized, and since the capacity of the unit is due largely to the outer portion of the disk and the face 2a of the cup, its sensitivity is increased bv providing the recessed portion 2,

It will be understood, of course, that the invention is not limited to the specic structure illustrated and described for the purpose, of disclosure but is capable of various modifications and changes while still adhering to the structural 1" eatures provided by the invention.

I claim:

l. A thermally responsive condenser for radioreceivers or the like, comprising a rigid member forming one element of the condenser, said member having an annular face and a centrally aperiured recessed portion, said member having an outwardly directed annular iiange about said aperture, an insulating member having a recess receiving said ange, a thermally-responsive bimetallic circular disk electrically insulated from said member for forming another element of the condenser, and means for securing the central portion of said disk to maintain the disk in proper spaced relation to said member, while permitting the disk to flex at its outer portions in response to ambient temperature variations, comprising an insulating sleeve and a securing element extending through said insulating member, said sleeve and said disk, said disk being closely adjacent to said annular face but spaced from said recessed portion.

2. A thermally responsive condenser for radio receivers or the like, comprising a rigid metallic member, said member having a central aperture, a thermally responsive bimetallic circular disk adjacent said member, an insulating sleeve extending axially of the condenser between said member and said disk for maintaining the disk in spaced relation to said member, an insulating member on the outer side of said metallic member, a metallic attachment element extending through the' center of the disk, through the said sleeve and the central aperture of said metallic member, and through said insulating member. and a terminal element secured by said attachment element against an outer face of said insulating membe'r for electrical connection to said disk.

3. A thermally responsive condenser for radio receivers or the like, comprising a rigid metallic member having a peripheral attachment lug for securing the condenser to a support and .for grounding said member at the support, said member having a central aperture, a iiange on said member about said opening extending trans-- versely from the member, a thermally responsive bimetallic circular disk adjacent the opposite side of said member, an insulating sleeve seated within said ange and extendng axially of the condenser between said member and said disk for maintaining the disk in spaced relation to said member, an insulating member on the outer side of said metallic member and having a recess seating said ange, said sleeve and said' 

